Emerging investigator series: influence of marine emissions and atmospheric processing on individual particle composition of summertime Arctic aerosol over the Bering Strait and Chukchi Sea

Abstract

Composition of individual atmospheric particles reveals the influence of marine sources, terrestrial sources, and anthropogenic sources on atmospheric chemistry in the changing Alaskan Arctic.

Simultaneous Optical Photothermal Infrared (O-PTIR) and Raman Spectroscopy of Submicrometer Atmospheric Particles

“…Ambient particles were analyzed with O-PTIR+Raman for the first time. Particles containing ammonium nitrate were identified by IR modes at 1351 and 1411 cm –1 , indicative of ν a (NO 3 – ) and δ­(NH 4 + ), respectively (Figure A). , The same particle contained Raman modes at 1068 and ∼3150 cm –1 , representing ν­(NO 3 – ) and ν­(N–H), respectively. ,, The agreement between IR and Raman provide robust evidence for the presence of ammonium nitrate, much stronger than either IR or Raman would provide independently due to common peaks in similar regions (e.g., organosulfates ∼1065 cm –1 in Raman). , Similarly, ambient sulfate-containing particles were identified by ν as (SO 4 2– ) at 1107 cm –1 in the IR spectrum , and ν s (SO 4 2– ) at 990 cm –1 in the Raman spectrum (Figure C). ,, This particle also contained organic modes identified as δ­(C–H) in the IR spectrum and ν­(C–H), ν­(CH 2 ), and δ­(CH 2 ) in the Raman spectrum, , similar to mixtures of sulfate and organic material identified in ambient particles with AFM-PTIR ,, and Raman. ,, Additional organic vibrational modes were identified in both IR and Raman spectra of ambient particles (Figure B), resembling modes detected in oxalate, sucrose, and SDS , (Figure ). OPTIR+Raman spectra show that significant chemical detail can be obtained from atmospheric particles containing complex mixtures of chemical species …”

“…2− ) at 990 cm −1 in the Raman spectrum (Figure 4C). 21,31,64 This particle also contained organic modes identified as δ(C−H) in the IR spectrum 66 and ν(C−H), ν(CH 2 ), and δ(CH 2 ) in the Raman spectrum, 67,68 similar to mixtures of sulfate and organic material identified in ambient particles with AFM-PTIR 39,43,69 and Raman. 19,28,34 Additional organic vibrational modes were identified in both IR and Raman spectra of ambient particles (Figure 4B), resembling modes detected in oxalate, 70 sucrose, 68 and SDS 24,66 (Figure 3).…”

“…Atomic force microscopy coupled to photothermal infrared spectroscopy (AFM-PTIR) has recently been applied to study particles and their chemical properties − by providing information on vibrational modes in particles down to 100 nm diameter. , The basic principle of AFM-PTIR is that a tunable IR laser, such as an optical parametric oscillator (OPO), scans across the mid-IR (i.e., 800–3600 cm –1 ), while an AFM tip is in contact with a particle or surface. ,− When the laser at a specific wavenumber excites a vibrational mode of a molecular species in the sample, the sample heats and slightly expands. ,, This photothermal expansion is detected by the AFM tip at each frequency as the laser source is scanned across the spectral range to produce an IR spectrum. The relationship between IR absorption and photothermal expansion detected by the AFM-PTIR tip is shown in eq : where u (t) is the time-dependent photothermal expansion of the sample in m 2 , a is the area of the heated region in m 2 (e.g., sphere = circle = radius, cube = square = edge length), G is a geometric constant based on the shape of the sample (e.g., sphere or cube), α T is the thermal expansion coefficient of the sample in K –1 , and ΔT (t) is the time-dependent temperature increase of the sample in K .…”

Probing Individual Particles Generated at the Freshwater–Seawater Interface through Combined Raman, Photothermal Infrared, and X-ray Spectroscopic Characterization

“…In addition, some of the modes from 1004 to 1015 could be from calcium sulfate or magnesium sulfate, which often co-locate during drying on the substrates . Sulfate has been identified as a component in nascent SSA in some studies, , though it is more prevalent in aged SSA following chlorine depletion and sulfur enrichment. − Notable absences from the Raman spectra include modes characteristic of phosphate (940–960 cm –1 ), ,, bisulfate (1040–1053 cm –1 ), , nitrate (1040–1068 cm –1 ), , carbonate (1065–1094 cm –1 ), , ammonium (1410–1417 cm –1 , though this ammonium mode is only weakly Raman active), , and CO esters (1736 cm –1 ) . A list of Raman mode assignments is given in Table S2.…”

Aerosol Acidity: Novel Measurements and Implications for Atmospheric Chemistry

“…This photothermal effect is detected by the AFM tip, and a spectrum is obtained by processing the change in deflection. Our group was the first to apply AFM-PTIR to atmospheric aerosols in Bondy et al We have continued to use AFM-PTIR, , as have several other research groups, , to study a range of environmental questions ranging from Arctic aerosol composition to indoor surface chemistry to pH. In Olson et al, we recently were the first to probe aerosol particles with optical PTIR (O-PTIR) with simultaneous Raman microspectroscopy.…”